Method and apparatus for improving metallic coatings



A 23, 1950 J. c. SLATER ETAL METHOD AND APPARATUS FOR IMPROVING METALLICCOATINGS 2 Sheets-Sheet 1 7 Filed July 7, 1958 INVENTORS. JOSEPH CI 5 42- 1 Aug. 23, 1960 J. c. SLATER EI'AL 2,950,215

METHOD AND APPARATUS FOR IMPROVING METALLIC COATINGS Filed July 7, 19582 Sheets-Sheet 2 INVENTORS. r/assnv C 52.47!

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METHOD AND APYPARATUS FOR INIPROVING NETALLIC CfiATlNGS Joseph C.Slater, Butler County, and Edward W. Platt, Butler, Pa, assignors toArrnco Steel Corporation, Middletown, Ulric, a corporation of Ohio FiledJuly 7, 1953, Ser. N 746,772

13 Claims. (Cl. 117-414) This invention relates to a method andapparatus for improving metallic coatings and is a continuationin-partof application Serial No. 322,690, filed November 26, 1952, nowabandoned, entitled Method and Apparatus for Improving MetallicCoatings. More specifically, the instant invention has to do with amethod and apparatus for insuring the uniform and even coating of ametallic strip when such metallic strip is fed through a pot containingmolten coating metal.

In the coating of metal strip with a layer of another metal, it has beenconventional practice to provide a pot of molten coating metal, the pothaving near the bottom thereof a so-called pot roll. The strip to becoated has been led into the pot and passed around the pot roll and thenled out of the pot between so-called exit rolls or wipers whichgenerally have for their purpose the removal of excess coating metal sothat a uniform coating of a desired weight can be obtained. In variouscoating procedures it is often found that a sort of scum forms on thesurface of the molten coating metal and that this scum adheres to thestrip as it passes into the coating bath with the result that thecoating metal does not adhere uniformly to the strip. The scum particlespicked up by the strip form a barrier on the strip which prevents thecoating metal from bonding to the strip, with the result that there is aconsiderable amount of unsatisfactorily coated metal which must berejected.

This problem is particularly apparent in coating processes wherein thestrip passes into the coating bath through a controlled atmosphere. Ithas been found that such atmospheres, while inert with respect to theclean strip surface, are not inert with respect to the surface of themolten coating metal. The atmospheres react rapidly with the moltenmetal forming scums on its surface. These scums adhere to the strip andare pulled through the coating bath with the result that the continuityof the coating is spoiled by uncoated areas.

We have observed that the foregoing phenomenon takes place continuouslyand is decidedly more pronounced if the strip is allowed to vibrate. Thefrequency and size of the scum particles adhering to the strip surfaceunder vibrating conditions is substantially greater and damage to theformation of a uniform bond is substantially more severe. In some casescompletely uncoated areas are produced resulting in intolerablerejection losses.

With the foregoing considerations in mind, it is an object of thepresent invention to provide a method and apparatus whereby such scumsas are picked up by the strip and carried into the bath are removed fromthe strip on both sides so that an even and continuous coating isprovided.

A principal object of the present invention is the provision of a methodand apparatus which provides for substantially vibration-free passage ofthe strip through the coating bath which results in a significantdecrease in scum pick-up. Coupled with this objective, a further objectof the invention is the provision of efiective scum wiping on both sidesof the strip while the strip is well within the confines of the coatingbath, the wiping of the strip serving to remove existing scum depositsat a sufiiciently early stage to permit proper recoating and bonding ofthe wiped areas.

It is a further object of the present invention to utilize the presentlyconventional coating pot and to provide by a simple expedient means forwiping both sides of the strip, and in which the means for Wiping oneside of the strip may comprise the presently conventional pot roll.

Still a further object of the invention is to provide an apparatus alongthe lines outlined above which is essentially the metal coating pot wellknown today with relatively minor modifications which are inexpensive toinstall and which in no Way affect the speed of production.

The foregoing together with other objects of the invention, which willbe pointed out in greater detail hereinafter, or which will be apparentto one skilled in the art upon reading these specifications, weaccomplished by those constructions and arrangements of parts, and bythat series of method steps, of which We shall now describe certainexemplary embodiments.

Reference is now made to the drawings forming a part hereof, andwherein:

Figure 1 is a vertical cross-sectional view through a typical metalcoating pot illustrating one form of the invention.

Figure 2 is a fragmentary cross-sectional view taken along the line 2--2of Figure 1.

Figure 3 is a fragmentary cross-sectional view taken along the line 3-3of Figure 1.

Figure 4 is a vertical cross-sectional view illustrating a modified formof metal coating pot.

Figure 5 is a vertical cross-sectional view illustrating still anothermodification of the invention.

Briefly, in the practice of the invention, means are provided under thesurface of the molten metal in the coating pot for wiping both surfacesof the strip as it passes through the pot. At least one of the wipingmeans will be placed within the bath and positioned to contact the stripas it moves downwardly in the bath, such wiping member serving theadditional function of dampingthe vibration of the incoming strip. Sinceit is conventional to pass the strip under a pot rollwhich serves as aguide member to change the direction of travel of the stripone form ofthe invention contemplates the provision of means to immobilize the potroll to prevent its rotation so that the pot roll itself serves to dampthe vibration of the strip and at the same time wipes the strip on oneside as the strip passes around the surface of the pot roll. A secondwiping means is also provided within the pot for the other side of thestrip over which the strip passes in frictional contact.

Thus, as seen in Figure 1 of the drawings, a metal coating pot isindicated generally at 10. A so-called exit machine is indicatedgenerally at 11, and it includes exit rolls 12 between which the strippasses as it emerges from the pot 10. The pot. 10, as will be readilyunderstood, contains a body of molten coating metal indicated at 13.Adjacent the bottom of the pot there is rotatably mounted the usual potroll 14 about which the strip 15 passes to make certain that the strippasses well under the surface of the coating metal.

In the particular embodiment illustrated the strip 15 enters the coatingpot through a duct 16 within which a controlled atmosphere ismaintained. The particular coating procedure is not important to thepresent invention since even where a controlled atmosphere is in contactwith the surface of the coating metal, a scum of indeterminatecomposition is often formed. This scum frequently adheres to the stripby a mechanical attachment and results in areas which are not coated bycoating metal. It has been found that this scum can be removed from thestrip by suitable wipers immersed in the coating metal.

It has also been noted that the mechanical attach ment of the scummaterial is aggravated by vibrations of the strip whichare'transnn'tted-to it by various pieces of apparatus outside the pot,including coilers, conveyor rollersandthelike. y 7 '7 7 According to thepresent aspect of the invention, and as best seen in Figure 2, the shaft17 which carries the pot roll 14 is provided with a gear 18 positionedoutside the pot where it is readily accessible; and in association withthis gear, means are provided for preventing rotation of the pot roll14. These means may include a bracket 19 with a stop plate 20 which maybe held out of contact with the gear 18 by means of a screw'21, andwhich upon release of the screw 21 willdrop downwardly intocontact'withrthe teeth of the gear 18 andthus hold the roll 14 againstrotation. It will be clear that when the roll 14 does not rotate, thestrip in passing-around the roll 14 will be wiped on the side which isin contact with the pot roll. At the same time, the pot roll serve todamp the vibration of the strip by means of the positive contact betweenthe strip and the immobilized roll. An additional wiper member 22 ispositioned between the pot roll and the exit rolls 12, the wiper member22 taking the form of a bar or roll welded or otherwise suitably securedto the bottom of the exit machine 11. It will be'noted from Figure 1that the wiper member 211is so positioned that the path' of the stripexiting from the pot is distorted from a line passing betweenthe exitrolls 12 and tangent to the pot roll 14. Preferably, the displacementofthe strip amounts to about /2" from the normal pass line, but thespecific amount of'distortion does not appear to be critical; It will beclear that the strip in passing over the non-rotatable member 22 iswiped on its other side. V i V The structure just described performs twofunctions, both of which are desirable. j In the first place, the stripin passing over the non-rotatable pot roll and rubbing against thewiping member 22 is steadied so that vibrations on the outside of thepot, eitherfrom cooling or coiling apparatus, are not carried throughinto the pot. The reduction of vibration has, as already indicated, theeflect of minimizingthe deposit of scum on the strip. Additionally, therubbing actionof the members 14 and 22 on the strip wipe 01f the scumwhich has attacheditself to the'strip at the-controlledatmospherecoating metal interface. Since the adherent scum or smudge is wiped ofi?both surfaces, the coating'metal is uniformly.

and evenly deposited on both surfaces of the strip and,

by reason of the fact that both wiping members are well.

within the confines of the pot, the strip will remain .in contact withthe coating metal for a sufiicient length of time to allow properreformation of the bond throughout the entire surface of the stripwithout interfering with the functioning of the exit rolls incontrolling the weight and uniformity of the coating. In thisconnection, it may be observed that if the strip is not thoroughlycleansed of scum by the time it reaches the exit rolls, the exit rollsact to smear the scum over adjoining properly coated 1areas of the stripand hence further aggravate the prob- In the practice of the invention,the stop 20 is retracted so that the pot roll mayrotate while the stripis being fed through the pot. .Assoonas the ship has been threadedthrough and the coating operation is ready to begin, the stop 20 will belowered into contact with the gear 18 and further rotation of the potroll 14 prevented; While it has been found that there isno appreciableaccumulation of scum on the wiping elements 14 and 22 during therelatively short time between replacement of the exit machine,nevertheless, if it should be found under certain conditions thatsome'of the scum deposits on these membersthey can beireadilycleaned.Thus, for example, the bottom pot roll may be permitted'to rotate,

I for a few revolutions, while the exit machine can be tilted so as toshift the member 22 out of contact with the strip. These expedients havenot, however, been found necessary in actual practice.

It will be clear that the particular means for preventing rotation ofthe pot roll 14 is not critical, and numerous modifications can be madetherein. Similarly, the wiper member 22 need not be a non-rotatablecylindrical object, but could bea plate or blade. Similarly the locationof wiper 22 may be altered. Thus, the member 22 could be placed ahead ofthe pot roll, in which event the wiper would be first contacted by thestrip and would serve to damp its vibration. Actually, the wiper for oneside of the strip need not be the pot roll at all, excepting for thefact that conventional metal coating apparatuses are provided with potrolls making it possible to utilize the invention with only very minormodifications of the existing equipment.

In Figure 4 there is illustrated a modification of the invention whereinthe pot roll 14a is permitted to revolve, and wherein the damping of thestrip is'accomplished by placing a wiper bar 23 on the entering side ofthe coating apparatus ahead of the pot roll 14a. With this arrangement,the wiper bar 23 will'wipe one side of the strip, and the other side maybewiped by the wiping member 22. i f

It is also possible to wipe both' sides'of'the strip by suitable wipingmeans installed on the entry side of the bath. Thus, as seen in. Figure5, an additional wiping member 24 may be positioned adjacent the wiper23 for contact with the opposite'side vof the strip. With thisarrangement, both sides of the strip are wiped prior to the passage ofthe strip around the pot roll 14a which, as in the embodiment of Figure4, will be free to rotate. It will be evident that the addition of thewiping members 23 or 24 to'the coating pot is a relatively simple matterand does not require any major modification of existing equipment.

i It will be clear from the foregoing that numerous modifications may bemade in the inventionwithout departing from the spirit of it, and itwill be therefore understood that we do not intend to limit ourselvesotherwise than as set forth in the claims which follow.

Having now fully described our invention in several exemplaryembodiments, what we claim as. new and desire to secure by LettersPatent is: i

1. In apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing a bathofmolten coating metal and is first led downwardly through the coatingmetal toward the bottom of the pot and then upwardly therethrough so asto emerge from the'bath between exit rolls; a first stationary wipingmember fixedly mounted .within the pot beneath the surface of the moltencoating metal and positioned to make full width contact with onejsideonly of the metallic strip, said first wiping member being of rigidnon-yielding construction and acting to deflect the strip from itsinitial downward direction of travel'so as to effectively dampenvibration of the strip as it enters the bath and at the same time effecta positive wiping action on the side of the strip contacted thereby, anda second rigid non-yielding wiping member fixedly mounted within saidpot beneath the surface of the bath intermediate said first wipingmember and the exitrolls,'said last named wiping member being positionedto make full width contact with the remaining side of the strip anddeflect it in the opposite direction, whereby to effect a positivewiping action on the remaining side of the strip.

2. The apparatus claimed in claim 1 wherein said first named \m'pingmember comprises a pot roll, wherein means are provided to preventrotation of said pot roll, and wherein said second wiping member islocated within the pot intermediate said pot roll and the exit rolls. j3. The apparatus claimed in claim 1 wherein one of said wiping memberscomprises a pot'roll located within said pot roll, and wherein means areprovided to prevent free rotation of said pot roll.

4. The apparatus claimed in claim 3 wherein said pot roll comprises saidsecond named wiping member.

5. In an apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing moltencoating metal, passes downwardly through the coating metal and around apot roll and then emerges from the coating metal between exit rolls;wiping means positioned in the pot for contact by the strip after it hasentered the molten coating metal and is moving downwardly therethrough,said wiping means comprising a pair of rigid non-yielding wiping memberspositioned ahead of the pot roll and arranged in non-opposed relation soas to sequentially contact opposite side of the strip and deflect itfirst in one direction and then in the other, whereby to eflectivelydamp the vibration of the strip as it passes downwardly through thecoating metal and at the same time efiect a positive wiping action onfirst one side of the strip and then the other.

6. In the coating of metallic strip with a layer of another metal bypassing said strip through a bath of molten coating metal, a method forimproving the quality of said coating which includes the steps ofadvancing the strip downwardly into the bath of molten coating metaland, as the strip is moved downwardly, drawing one side of the stripacross the surface of a rigid non-yielding wiping member fixedly mountedwithin the bath and positioned to deflect the strip in one direction asit is drawn over the rigid wiping member, and thereafter drawing theopposite side of the strip over a second rigid non-yielding wipingmember also located within the bath, said second wiping member lyingbeyond the first named wiping member and positioned to deflect the stripin the opposite direction, and then withdrawing the strip from the bathand, as the strip emerges from the bath, passing it through a finishingmeans effective to control the weight and uniformity of the coatingthereon.

7. In an apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing moltencoating metal, passes around a pot roll and then emerges from the potbetween exit rolls; means to prevent the rotation of said pot rollwhereby said strip in passing around said pot roll will be wiped on oneside, and wiping means in said pot for the other side of said strip,said last named wiping means being positioned to displace said stripfrom its normal path of travel through said pot.

8. In an apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing moltencoating metal, passes around a pot roll and then emerges from the potbetween exit rolls, said pot roll having a shaft extending out of saidpot; means accessible on the outside of said pot to prevent rotation ofsaid pot roll, whereby said strip in passing around said pot roll willbe wiped on one side, and wiping means in said pot for the other side ofsaid strip, said last named wiping means being positioned to displacesaid strip from its normal path of travel through said pot.

9. In an apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing moltencoating metal, passes around a pot roll and then emerges from the potbetween exit rolls, said pot roll having a shaft extending out of saidpot; a gear on said shaft outside said pot, and means selectivelyengageable with said gear to prevent rotation of said pot roll, wherebysaid strip in passing around said pot roll will be wiped on one side,and wiping means in said pot roll for the other side of said strip, saidlast named wiping means being positioned to displace said strip from itsnormal path of travel through said pot.

10. In an apparatus for coating metallic strip with a layer of anothermetal, wherein the strip to be coated enters a pot containing moltencoating metal, passes around a pot roll and then emerges from the potbetween exit rolls; means to prevent the rotation of said pot roll,whereby said strip in passing around said pot roll will be wiped on oneside, and cylindrical wiping means in said pot for the other side ofsaid strip, said last named means being positioned to displace saidstrip from its normal path of travel through said pot.

11. In the coating of metallic strip with a layer 01 another metal bypassing said strip through a bath of molten coating metal having a potroll in the bath, the method of improving the quality of said coatingwhich includes the steps of holding said pot roll against rotation tocause the side of the strip contacting the pot roll to be wiped, andwiping the other side of the strip by causing it to pass in frictionalcontact with a second wiping surface located under the surface of saidbath.

12. In the coating of metallic strip with a layer of another metal bypassing the said strip through a bath of molten coating metal having apot roll located within the bath, the method of improving the quality ofthe coating which includes the step of feeding the strip into the bathand causing it to pass around said pot roll, whereby to change thedirection of movement of the strip, wiping at least one side of thestrip by means of a rigid stationary wiper positioned to contact anddeflect the strip prior to its change in direction, and wiping theremaining side of the strip at least prior to the time it emerges fromthe said bath by means of a second rigid wiper positioned to contact anddeflect the said strip.

13. In the coating of metallic strip with a layer of another metal bypassing the strip through a bath of molten coating metal, the method ofimproving the quality of said coating which includes the step of movingthe strip downwardly into the bath in a first direction of movement and,while the strip is moving in said first direction, wiping at least oneside of the strip against a first rigid wiper positioned to deflect thestrip as it moves downwardly in said pot, thereafter causing the stripto change its direction of movement so as to move upwardly through thebath toward an exit station, wiping the remaining side of the stripagainst a second rigid wiper positioned at a point within the bath wellin advance of said exit station and, as the strip passes through saidexit station, contacting both sides thereof with a finishing meanseflective to control the weight and uniformity of the coating thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,479Brown Mar. 4, 1842 1,053,664 Sommer Feb. 18, 1913 1,933,401 Ward Oct.31, 1933 2,093,857 Williamson Sept. 21, 1937 2,394,545 Grupe Feb. 12,1946 2,398,034 Organowski Apr. 9, 1946

11. IN THE COATING OF METALLIC STRIP WITH A LAYER OF ANOTHER METAL BYPASSING SAID STRIP THROUGH A BATH OF MOLTEN COATING METAL HAVING A POTROLL IN THE BATH, THE METHOD OF IMPROVING THE QUALITY OF SAID COATINGWHICH INCLUDES THE STEPS OF HOLDING SAID POT ROLL AGAINST ROTATION TOCAUSE THE SIDE OF THE STRIP CONTACTING THE POT ROLL TO BE WIPED, ANDWIPING THE OTHER OF THE STRIP BY CAUSING IT TO PASS IN FRICTIONALCONTACT WITH A SECOND WIPING SURFACE LOCATED UNDER THE SURFACE OF SAIDBATH.